Design random id generator

requirements:
- id limited to 64 bits
- id is increased by date

single machine
- integer? hard to scale to multiple server case

one ticket server
- bottle neck

multiple server
-each server with a id / o ruse mac address
-guid: random or mac+timestamp
- twitter's snowflake

clock  synchronization
-NTP


reference:
http://www.slideshare.net/davegardnerisme/unique-id-generation-in-distributed-systems

• Announcing Snowflake
• snowflake.

flickr's ticket server:  http://code.flickr.net/2010/02/08/ticket-servers-distributed-unique-primary-keys-on-the-cheap/